Evidence of structural cavities in 3D printed acetabular cups for total hip arthroplasty

Effects of Vancomycin/Tobramycin-Doped Ceramic Composite (Polyvinyl Alcohol Composite-Vancomycin/Tobramycin-Polymeric Dicalcium Phosphate Dihydrate) in a Rat Femur Model Implanted With Contaminated Porous Titanium Cylinders

BACKGROUND

Periprosthetic joint infection (PJI) remains common and problematic. We hypothesized that using a bioceramic that provided rapid release of the antibiotics (vancomycin [VAN] or VAN and tobramycin [VAN and TOB]) from a polyvinyl-alcohol-composite (PVA) combined with a delayed and sustained antibiotic release from polymeric-dicalcium-phosphate-dihydrate (PDCPD) ceramic would inhibit S. aureus-associated implant infections.

METHODS

A total of 50 male Sprague Dawley rats were randomly divided into 5 groups-I: negative control; II: bacteria only; III: bacteria + saline wash; IV: bacteria + PVA-VAN-PDCPD, and V: bacteria + PVA-VAN-TOB-PDCPD. A porous titanium (Ti) implant was press-fit into the rat knee. S. aureus-containing broth was added into the joint space creating a PJI. After 1 week, the joints from groups III to V were washed with saline and the fluid collected for bacterial quantification. This was followed by saline irrigation treatment (groups III to V) and application of the antibiotic-loaded PVA-PDCPD bioceramic (groups IV and V). On day 21, joint fluid was collected, and the implants harvested for bacterial quantification.

RESULTS

No bacteria were isolated from the negative control (group I). The positive control (group II) was positive on both days 7 and 21. Bacteria were still present on day 21 in the fluid and implant in group III. Groups (IV and V) showed a decrease in the bacterial burden in the fluid and implant on day 21. There were significant differences in bacteria levels in the collected wash fluid and on the implant at day 21 between the saline wash (group III) and treatment groups (IV and V).

CONCLUSIONS

In this animal model of acute periprosthetic infection, treatment with PVA-VAN-PDCPD and PVA-VAN/TOB-PDCPD reduced bacterial load in the infected joint and the infected Ti implant. Application of PVA-VAN-PDCPD and/or PVA-VAN/TOB-PDCPD after saline irrigation could be used as an addition to the treatment of PJI.

Effect of the Spatial Arrangement of Floating Builds with Minimum Support on the Microstructural and Mechanical Characteristics of Electron Beam Additively Manufactured Biomedical Ti-6Al-4V Alloys

In this study, normal and floating builds of Ti-6Al-4V were fabricated by electron beam additive manufacturing. The effects of the spatial arrangement on the microstructure, mechanical properties, and surface roughness of the parts were investigated. Both the normal and floating builds exhibited an α+β lamellar microstructure, but the normal builds had finer grains compared to the floating builds. The microstructural characteristics were correlated with the thermal history, specifically the cooling rate, resulting from the connection plate (S45C for the normal builds and the powder bed for the floating builds). The compressive yield strength and hardness of the normal builds were higher than those of the floating builds, regardless of build location owing to the grain refinement effects on the normal builds. The top surface (TS) of the sample was smoothest, and the lateral surface of the sample was the roughest for both the normal and floating builds; however, the roughness of the TS and bottom surface samples did not differ significantly between normal and floating builds. There were no noticeable differences in the microstructure and mechanical properties of the builds in five different positions, that is, the center and four corners. Finally, these findings were used to develop a set of conceptual spatial arrangement designs, including floating builds, to optimize the microstructure and mechanical properties.

The Possibilities of Personalized 3D Printed Implants-A Case Series Study

Background and Objectives: Following the most recent software and 3D printing developments, the use of personalized 3D printed orthopedic implants for treatment of complicated surgical cases has gained more popularity. Today, orthopedic problems that cannot be solved with standard implants may be effectively addressed using personalized prostheses. The aim of this study is to present the designing, modeling and production stages of four different personalized 3D printed prostheses and their application in clinical cases of patients who underwent treatment in various anatomical locations with a precisely specified indication for implantation. Materials and Methods: Based on computed tomography scanning, personalized 3D printed prostheses were designed, produced and used in four patients within a period of three to five days after injury or admission. Results: Early term follow-ups demonstrated good to excellent results. Conclusions: Personalized 3D printed prostheses offer an opportunity for a treatment of choice and provide good anatomical and functional results, shortened surgical time, less complications, and high satisfaction in patients with appropriate indications. The method should be considered primarily for patients with large bone defects, or such indicated for resection. Personalized 3D printed prostheses have the potential to become more common and beneficial in the future.

The analysis of defects in custom 3D-printed acetabular cups: A comparative study of commercially available implants from six manufacturers

Three-dimensional (3D) printing is used to manufacture custom acetabular cups to treat patients with massive acetabular defects. There is a risk of defects occurring in these, often in the form of structural voids. Our aim was to investigate the presence of voids in commercially available cups. We examined 12, final-production titanium custom acetabular cups, that had been 3D-printed by six manufacturers. We measured their mass, then performed micro-computed tomography (micro-CT) imaging to determine their volume and density. The micro-CT data were examined for the presence of voids. In cups that had voids, we computed (1) the number of voids, (2) their volume and the cup volume fraction, (3) their sphericity, (4) size, and (5) their location. The cups had median mass, volume, and density of 208.5 g, 46,471 mm³ , and 4.42 g/cm³ , respectively. Five cups were found to contain a median (range) of 90 (58-101) structural voids. The median void volume and cup volume fractions of cups with voids were 5.17 (1.05-17.33) mm³ and 99.983 (99.972-99.998)%, respectively. The median void sphericity and size were 0.47 (0.19-0.65) and 0.64 (0.27-8.82) mm, respectively. Voids were predominantly located adjacent to screw holes, within flanges, and at the transition between design features; these were between 0.17 and 4.66 mm from the cup surfaces. This is the first study to examine defects within final-production 3D-printed custom cups, providing data for regulators, surgeons, and manufacturers about the variability in final print quality. The size, shape, and location of these voids are such that there may be an increased risk of crack initiation from them.

Morphometric analysis of patient-specific 3D-printed acetabular cups: a comparative study of commercially available implants from 6 manufacturers

Background

3D printed patient-specific titanium acetabular cups are used to treat patients with massive acetabular defects. These have highly porous surfaces, with the design intent of enhancing bony fixation. Our aim was to characterise these porous structures in commercially available designs.

Methods

We obtained 12 final-production, patient-specific 3D printed acetabular cups that had been produced by 6 manufacturers. High resolution micro-CT imaging was used to characterise morphometric features of their porous structures: (1) strut thickness, 2) the depth of the porous layer, (3) pore size and (4) the level of porosity. Additionally, we computed the surface area of each component to quantify how much titanium may be in contact with patient tissue. Statistical comparisons were made between the designs.

Results

We found a variability between designs in relation to the thickness of the struts (0.28 to 0.65 mm), how deep the porous layers are (0.57 to 11.51 mm), the pore size (0.74 to 1.87 mm) and the level of porosity (34 to 85%). One manufacturer printed structures with different porosities between the body and flange; another manufacturer had two differing porous regions within the body of the cups. The cups had a median (range) surface area of 756.5 mm² (348 – 1724).

Conclusions

There is a wide variability between manufacturers in the porous titanium structures they 3D print. We do not currently know whether there is an optimal porosity and how this variability will impact clinically on the integrity of bony fixation; this will become clearer as post market surveillance data is generated.

Functionally graded additive manufacturing for orthopedic applications

Background

Additive Manufacturing due to its benefits in developing parts with complex geometries and shapes, has evolved as an alternate manufacturing process to develop implants with desired properties. The structure of human bones being anisotropic in nature is biologically functionally graded i,e. The structure possesses different properties in different directions. Therefore, various orthopedic implants such as knee, hip and other bone plates, if functionally graded can perform better. In this context, the development of functionally graded (FG) parts for orthopedic application with tailored anisotropic properties has become easier through the use of additive manufacturing (AM).

Objectives

and Rationale: The current paper aims to study the various aspects of additively manufactured FG parts for orthopedic applications. It presents the details of various orthopedic implants such as knee, hip and other bone plates in a structured manner. A systematic literature review is conducted to study the various material and functional aspects of functionally graded parts for orthopedic applications. A section is also dedicated to discuss the mechanical properties of functionally graded parts.

Conclusion

The literature revealed that additive manufacturing can provide lot of opportunities for development of functionally graded orthopedic implants with improved properties and durability. Further, the effect of various FG parameters on the mechanical behavior of these implants needs to be studied in detail. Also, with the advent of various AM technologies, the functional grading can be achieved by various means e.g. density, porosity, microstructure, composition, etc. By varying the AM parameters. However, the current limitations of cost and material biocompatibility prevent the widespread exploitation of AM technologies for various orthopedic applications.

Application of three-dimensional printing technology in peripheral hip diseases

The incidence of peripheral hip diseases is increasing every year, and its treatment is always tricky due to the complexity of hip joint anatomy and a variety of surgical methods. This paper summarizes the application research and progress of three-dimensional (3D) printing technology in different peripheral hip diseases in recent years published by PubMed from January 2017 to July 2021 with the search terms including “3D or three-dimensional, print*, and hip*. In general, the application of 3D printing technology is mainly to print bone models of patients, make surgical plans, and simulate pre-operation, customized surgical navigation templates for precise positioning or targeted resection of tissue or bone, and customized patient-specific instruments (PSI) fully conforms to the patient’s anatomical morphology. It mainly reduces operative time, intraoperative blood loss, and improves joint function. Consequently, 3D printing technology can be customized according to the patient’s disease condition, which provides a new option for treating complex hip diseases and has excellent application and development potential.

Osseointegration of retrieved 3D-printed, off-the-shelf acetabular implants

Aims

The main advantage of 3D-printed, off-the-shelf acetabular implants is the potential to promote enhanced bony fixation due to their controllable porous structure. In this study we investigated the extent of osseointegration in retrieved 3D-printed acetabular implants.

Methods

We compared two groups, one made via 3D-printing (n = 7) and the other using conventional techniques (n = 7). We collected implant details, type of surgery and removal technique, patient demographics, and clinical history. Bone integration was assessed by macroscopic visual analysis, followed by sectioning to allow undecalcified histology on eight sections (~200 µm) for each implant. The outcome measures considered were area of bone attachment (%), extent of bone ingrowth (%), bone-implant contact (%), and depth of ingrowth (%), and these were quantified using a line-intercept method.

Results

The two groups were matched for patient sex, age (61 and 63 years), time to revision (30 and 41 months), implant size (54 mm and 52 mm), and porosity (72% and 60%) (p > 0.152). There was no difference in visual bony attachment (p = 0.209). Histological analysis showed greater bone ingrowth in 3D-printed implants (p < 0.001), with mean bone attachment of 63% (SD 28%) and 37% (SD 20%), respectively. This was observed for all the outcome measures.

Conclusion

This was the first study to investigate osseointegration in retrieved 3D-printed acetabular implants. Greater bone ingrowth was found in 3D-printed implants, suggesting that better osseointegration can be achieved. However, the influence of specific surgeon, implant, and patient factors needs to be considered.

Cite this article: Bone Joint Res 2021;10(7):388–400.

Off-the-shelf 3D printed titanium cups in primary total hip arthroplasty

Three-dimensional (3D)-printed titanium cups used in primary total hip arthroplasty (THA) were developed to combine the benefits of a low elastic modulus with a highly porous surface. The aim was to improve local vascularization and bony ingrowth, and at the same time to reduce periprosthetic stress shielding. Additive manufacturing, starting with a titanium alloy powder, allows serial production of devices with large interconnected pores (trabecular titanium), overcoming the drawbacks of tantalum and conventional manufacturing techniques. To date, 3D-printed cups have achieved dependable clinical and radiological outcomes with results not inferior to conventional sockets and with good rates of osseointegration. No mechanical failures and no abnormal ion release and biocompatibility warnings have been reported. In this review, we focused on the manufacturing technique, cup features, clinical outcomes, open questions and future developments of off-the-shelf 3D-printed titanium shells in THA.

A New Additive-Manufactured Cementless Highly Porous Titanium Acetabular Cup for Primary Total Hip Arthroplasty-Early Two-Year Follow Up

INTRODUCTION

Additive-manufacturing technologies are increasingly being used, not only to create acetabular components with porous coating architecture very similar to the complex trabecular structure of cancellous bone, but also for producing the entire implant in a single step. The aim of this study is to assess two-year clinical and radiological outcomes of a new additive-manufactured cup in primary total hip arthroplasty (THA).

MATERIALS AND METHODS

We reviewed 266 primary THAs (254 patients) performed in our institution between December 2016 and December 2018 using a new highly porous titanium acetabulum shell fabricated via additive manufacturing. Clinical and functional outcomes were measured using SF/VR-12 and HOOS JR to determine patient satisfaction with surgery. Radiographs were assessed to determine the presence of migration, radiolucency, and loosening. Patients records were reviewed to assess cup survivorship in terms of all-cause revisions and revision for aseptic cup loosening.

RESULTS

At a minimum of two-year follow up (range: 2-3.45 years), the patient cohort demonstrated significant improvement in postoperative functional scores (hip disability and osteoarthritis outcome score for joint replacement [HOOS JR.] and clinical scores (12-item short-form health survey [SF/VR-12]) (p<0.001). One cup developed progressive radiolucent lines at the prosthesis-bone interface consistent with loosening and was revised. The overall acetabular component two-year survivorship free of all-cause failure was 97.4% (95% confidence interval [CI]: 95.5-99.4%). When aseptic loosening of the acetabular component was used as the failure endpoint, the two-years survivorship rate was 99.6% (95% CI: 98.9-100%).

CONCLUSION

Highly porous titanium cementless acetabular cups produced via additive-manufacturing showed promising early clinical and radiological results in primary THA with low rates of aseptic loosening. Further follow-up studies are needed to assess the long-term survivorship and outcomes of this new acetabular component.

Severe Corrosion of Modular Dual Mobility Acetabular Components Identified During Revision Total Hip Arthroplasty

There has been a significant increase in the use of modular dual mobility (MDM) acetabular cups for primary and revision total hip arthroplasty (THA) secondary to decreased dislocation rate and increased impingement-free range of motion. Mating of dissimilar metals in THA can result in mechanically assisted crevice corrosion, with increased serum metal ion levels and potentially adverse local tissue reaction that can lead to revision surgery. In this case report, we present a patient who had THA using MDM components, and his follow-up laboratory testing showed asymptomatic elevated serum cobalt level. The patient subsequently developed an intraprosthetic dislocation that required revision surgery. At the time of revision, significant corrosion was noted on the backside of the modular acetabular liner and the inner surface of the titanium shell. Serum cobalt levels returned to normal after revision surgery. This case suggests that mechanically assisted crevice corrosion at the modular surface of MDM components does occur. In addition, we believe surgeons should judiciously use MDM technology only for patients at significantly increased risk of dislocation after THA.